The starting materials used in the process according to the invention are oil in water emulsions comprising fats of dairy origin like, for example, milk or cream. Milk is a liquid secreted by mammalian glands of female mammals. It is composed of five major constituents:
lipids essentially in the form of triglycerides, PA0 proteins, PA0 glucids, PA0 salts, PA0 water.
Cream is in fact a milk enriched in fat by spontaneous scumming or centrifuging. It contains therefore the same major elements as milk but in different proportions.
These two products also comprise constituents present in very minimal amounts like lecithins, vitamins, enzymes, dissolved gases, the fatty acids present naturally in the milk and/or arising from the hydrolysis of triglycerides, and sterols. The latter are essentially represented by cholesterol to the extent of 98% and are substances associated with the fat. The fat of cows' milk contains about 0.3% of cholesterol namely 0.1 g per liter of milk.
Now it has been established for a long time that high blood levels of cholesterol (cholesterol LDL) are in direct correlation with serious cardio-vascular deseases.
The principal of these is arteriosclerosis which is manifested by the alteration of the wall of the arteries and of which one of the causes is the localized, excessive and abnormal deposit of cholesterol on the inner surface of the wall of an artery. The atheroma so formed can have tragic consequences like myocardial infarctus. By way of illustration, it may be indicated that a reduction of 1% of the total blood cholesterol results in a reduction of 2% of the coronary risk. The excess of cholesterol can also be the cause of gallstones.
Prevention remains one of the most effective means for remedying these pathologies. It can consist of reducing as much as possible the ingestion of foods rich in cholesterol or indeed also of consuming foodstuffs with a low cholesterol content.
One of the concerns of industrialists in the food industry is hence to eliminate the cholesterol from products of current consumption and particularly dairy products.
Thus there have already been proposed various methods of extraction of sterols from fats.
One of them consists of contacting the animal fat with digitonin which has the property of reacting with the cholesterol to give a precipitate. The performances and the results of this method are not satisfactory due to the fact of the difficulty of separation of the precipitate from the medium. This method is, in any event, inapplicable industrially.
The cholesterol can also be extracted from fats by entrainment by means of a solvent. The major drawback of this method is that the solvents generally employed are toxic and that traces of them always remain in the fats concerned.
There are also known methods of microdistillation, which are inapplicable at the industrial level, or again adsorption on columns, as is described, for example, in European patent application nos. EP n.degree. 0 174 848 and EP n.degree. 0 318 326. These applications teach a method according to which the fat kept in the liquid state passes through an adsorbent column, in the event activated charcoal. It is clear that such a process is very cumbersome to put into practice and, moreover, the extraction that it enables is not very selective.
Another physico-chemical process of extraction of the cholesterol from fats is disclosed by the Japanese patent application JP n.degree. 59/140299. It consists of contacting a dry substance charged with cholesterol such as milk powder, with supercritical CO.sub.2 at a temperature comprised between 35.degree. and 45.degree. C. and at a pressure comprised between 130 and 200 atm. The production of these physical conditions necessitates the employment of complex and expensive equipment. The management of the process is thus very delicate. Moreover, as is specified in the patent application, other lipid compounds are entrained by the supercritical CO.sub.2. This process is hence not selective.
To remove the sterols from fats, there has also been contemplated a process of biodegradation of said sterols disclosed by the patent application n.degree. EP 0 278 794 and employing bacteria which, contacted with the fat, are capable of metabolizing at least one of the sterols that it contains. Like all methods involving fermentations, this biodegradation process is very delicate to manage due to the fact of the inherent variability of living matter. In addition, the equipment employed, the relatively long duration, are, among other things, elements which render such a process expensive. Finally, the catabolites produced in these fermentations remain until now totally unknown on the level of their nature and their toxicity, and are, in any case, present in the fats so treated.
There is also known, through European patent application EP n.degree. 0 256 911, a process for removing cholesterol contained in animal fat. It is based on the property already disclosed of cyclic cyclodextrinspolyglucoses of frustoconic tubular conformation with 6, 7 or 8 glucose units and denoted respectively by alpha, beta or gamma- of receiving in their hydrophobic central cavity sterol molecules and especially cholesterol, to form water-soluble inclusion complexes. According to this process, the fat kept fluid is contacted with a cyclodextrin with stirring for 30 minutes to 10 hours so as to enable the formation of complexes. The separation of the latter is then carried out by introduction into the reaction medium of water which solubilizes these complexes. The aqueous solution thus obtained is then collected after decantation.
The efficiency of extraction of the cholesterol by this process is not great. In the best of cases, it is in fact only 41%, and this after 3 successive extractions, as is indicated in Example 3 of the description of this European patent application.
It is to be noted that by this process, the fat must be kept melted under an oxygen-free atmosphere. These technical characteristics imply recourse to a specific apparatus for maintaining temperature and supply of neutral gas. Lastly, the time necessary for the first complexation phase is a minimum of 30 minutes and actually from 2-3 hours as indicated in the example. This process is hence necessarily expensive in time, equipment and in energy.
Apart from these scarcely satisfactory performances this process constitutes a succession of additional steps in the manufacture of a foodstuff and forms part of an industrial procedure which is somewhat irrational. In fact it consists firstly of manufacturing the fat in anhydrous form, of making it undergo the cumbersome cholesterol extraction treatment, then of bringing it to a suitable state in which it will be utilizable in a process for producing foodstuffs. In the case of dairy fat, these foodstuffs can be reconstituted milks for consumption, yogurts, cheeses or the like. It is clear that such a scheme is not acceptable from the point of view of industrial profitability.
It is apparent from the foregoing that none of these solutions of the prior art has enabled until now the production of food fats impoverished in sterols-- especially in cholesterol, satisfactorily, that is to say, responding to the industrial conditions of economic profitability, flexibility of use, and quality of the final products.
In addition, with regard to this quality of the final products obtained by applying known processes, it is important to observe that these products, like any dairy fat, can be oxidized and become rancid, which makes them unsuitable for consumption. In fact, dairy fat comprises unsaturated compounds reacting very easily with the oxygen of the air. This is the reason why, in the process described in patent application EP n.degree. 0 256 911 mentioned above, there is provision for operating under nitrogen. But it remains nonetheless that the products so treated stay very strongly subject to becoming rancid, which inevitably undermines their food value.